4.2 General Design and Technical Guidance
A primary consideration in the design and construction of DoD
weapons systems or facilities is the proper blending of safety, affordability,
and environmental needs with mission and operational requirements. DoD systems
or facilities are expected to perform reliably, require minimum maintenance
over a specified lifetime, and deteriorate at rate that permits maximum
service life . Therefore, materials, manufacturing methods and protective
treatments which reduce failures due to deterioration should be considered
during the process of selecting suitable materials and appropriate
manufacturing methods that will satisfy system requirements. Deterioration
modes which contribute to failures include, but are not limited to, pitting
corrosion, galvanic corrosion, exfoliation corrosion, stress corrosion,
corrosion fatigue, thermal embrittlement, fretting fatigue, oxidation,
hydrogen embrittlement, weathering and fungus growth. Much background
information and directed research may be available through AMPTIAC. In the
entire design phase, attention should be given to precautionary measures to
minimize deterioration of individual parts and assemblies as well as the entire system. Precautionary measures are included in
the following paragraphs. The CPCP and program/project specifications should
detail specific requirements.
Fundamentally, the design should attempt to
eliminate corrosive contaminants. If materials are expected to be exposed to
contaminants, select design geometries, materials, manufacturing processes,
and coatings that prevent or control corrosion.
Selected design disciplines should enable
designers to evaluate the following general approaches to design: selecting
the right materials and manufacturing processes, applying protective coatings
as necessary, using proper corrosion preventative and control designs, and
modifying the environment.
If possible, avoid materials that are
unsuitable to the operational environment. Consider compatibility when using
multiple materials. If dissimilar materials cannot be avoided, isolate those
materials from each other.
Protective coatings should be considered to
isolate vulnerable materials from the environment.
Avoid crevices when possible. Avoid design
features that make it difficult for protective coatings to function (sharp
corners, for instance). Avoid geometries that unnecessarily trap
4.2.4 Modify the
When it is necessary for a portion of the
system to be exposed to the environment, consider a design which allows for
the modification of the environment to which materials will be exposed.
Dehumidification and sheltering can be effective means for modifying the